EPIDEMIOLOGIC RELATEDNESS AND CLONAL TYPES OF NATURAL-POPULATIONS OF ESCHERICHIA-COLI STRAINS PRODUCING SHIGA TOXINS IN SEPARATE POPULATIONS OF CATTLE AND SHEEP

Two separate animal populations consisting of a herd of cattle (19 ani mals) and a flock of sheep (25 animals) were investigated for strains of Escherichia coli producing Shiga toxins (STEC) over a time period o f 6 months. Thirty-three STEC were isolated from 63.2% of cattle and g rouped into II serotypes and eight electrophoretic types (ETs) by mult ilocus enzyme analysis. In sheep, 88% of the animals excreted STEC (n = 67 isolates) belonging to 17 different serotypes and 12 different ET s. STEC from cattle and sheep differed with respect to serotype, and o nly 4 of the 16 ETs occurred in both animal populations. In cattle, ET 14 (0116:1121) strains predominated, whereas other STEC serotypes occu rred only sporadically. The predominating STEC types in sheep were ET4 (0125 strains), ET11 (0128:112 and others), and ET14 (0146:H21). In c ontrast to their diversity, STEC originating from the same animal popu lation were similar with respect to Shiga toxin (stx) genes. Almost al l STEC isolated from cattle were positive for stx(2) and stx(2c); only one was positive for stx(1). In sheep, almost all STEC isolated were positive for stx(1) and stx(2), whereas stx(2c) was not found. XbaI-di gested DNAs of genetically closely related 0146:1121 strains have diff erent restriction profiles which were associated with size alterations in XbaI fragments hybridizing with stx(1)- and stx(2)-specific DNA pr obes. Our results indicate that stx-encoding bacteriophages might be t he origin of the genetic heterogeneity in STEC from animals.